The present invention is directed to an improved concrete material containing silica. The present invention also is directed to an improved blended cement conforming to the ASTM specifications of commercial standard C-595. Silica has previously been added to concrete in the form of a by-product from plants which produce magnesium and ferrosilicon, this by-product being known as "silica fume". Silica also is sometimes found in the raw materials such as limestone which are burned in the process for forming cement clinker. Silica in this form is an integral part of the portland cement clinker and does not perform in the same manner as the present invention.
Silica fume has found acceptance as an additive to increase the strength of concrete. However, silica fume suffers from disadvantages because of its relatively high cost and extreme difficulties in handling due to the extreme fineness of the material. In fact, the material can usually be transported to a job site only in bags or in some instances as a wet slurry. Thus, concrete which includes this silica strengthener has been considered as somewhat of a specialty product.
Moreover, the silica fume is considered to be a "thirsty" additive, increasing the water requirements to make the concrete workable. Additional water also reduces strength. Therefore, due to the increased water requirement, such concretes also require expensive water reducing chemicals to offset the extra water introduced for improving workability. Without the water reducing agents, the concrete has difficulty reaching its specified design strength.
The production of cement requires relatively large amounts of energy, much of it in the form of fossil fuels. Six to eight million BTU are normally required to produce one short ton (2000 lb) of finished cement. The provision of a component which would replace cement and thus reduce the overall amount of cement required in concrete would likewise reduce energy consumption in proportion to its use and also reduce the strain upon cement supplies. Similarly, proportional ecological benefits would be obtained through decreased emissions from cement production.